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For the millions of people who suffer from seasonal allergies, springtime means runny noses, excessive sneezing, and itchy eyes. And, as with many things, climate change seems to be making allergy season even worse. Researchers’ reports Earth and Space Chemistry ACS showed that common allergen plants such as ryegrass and ragweed emit smaller ‘substantial particles’ (SPPs) than previously thought, yet climate is likely more affected by intact pollen grains, which can promote cloud formation.
In addition to annoying sinuses, pollen naturally serves as a way for plants to exchange genetic material and reproduce. When exposed to moisture, pollen grains can burst into tiny SPPs less than a micron in length. Their small size allows them to reach the lower respiratory tract, where they can last longer and cause more inflammation than their larger counterparts. Both SPPs and whole pollen grains are also thought to act as ice nucleation sites – miniature springboards for clouds. But compared to normal clouds, SPPs and pollen form smaller, more numerous clouds that tend to hold on to precipitation, helping to trap radiant heat and contributing to climate change. In contrast, higher temperatures can lengthen pollen release periods, exacerbating the problem. Previously, Brianna Matthews, Alyssa Alsante, and Sarah Brooks studied how oak trees emit SPPs at different moisture levels. This time, however, the team wanted to investigate how two other common allergen-producing plants, ragweed and ryegrass, secrete SPPs under wet conditions, and how these particles might affect the formation of ice clouds.
The researchers collected samples of ryegrass and ragweed, then placed them in a specialized “pollen chamber.” There, the samples were exposed to different humidity levels and bursts of wind over several hours to simulate real-world conditions.
The group evaluated the number of SPPs per pollen grain, as well as the ice-nucleating abilities of both. Surprisingly, the team found that previous experiments on the same types of plants underestimated the amount of SPPs by a factor of 10 to 100. This was likely because other experiments used less realistic means of spreading pollen and generating SPPs, the researchers say. Ragweed and ryegrass SPPs were too weak to nucleate with ice, however – hardly better than plain water – while whole pollen facilitated the growth of clouds. The researchers say that these updated parameters and the numbers of pollen released and particles can eventually be used to create more accurate climate models.
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